The magnetic asymmetry effect in geometrically asymmetric capacitively coupled radio frequency discharges operated in Ar/O₂

Abstract

Previous studies in low pressure magnetized capacitively coupled radio frequency (RF) plasmas operated in argon with optimized geometric reactor symmetry have shown that the magnetic asymmetry effect (MAE) allows to control the particle flux energy distributions at the electrodes, the plasma symmetry, and the DC self-bias voltage by tuning the magnetron-like magnetic field adjacent to one electrode (Oberberg et al 2019 Plasma Sources Sci. Technol. 28 115021; Oberberg et al 2018 Plasma Sources Sci. Technol. 27 105018). In this way non-linear electron resonance heating (NERH) induced via the self-excitation of the plasma series resonance (PSR) was also found to be controllable. Such plasma sources are frequently used for reactive RF magnetron sputtering, but the discharge conditions used for such applications are significantly different compared to those studied previously. A high DC self-bias voltage (generated via a geometric reactor asymmetry) is required to realize a sufficiently high ion bombardment energy at the target electrode and a reactive gas must be added to deposit ceramic compound layers. Thus in this work, the MAE is investigated experimentally in a geometrically asymmetric capacitively coupled RF discharge driven at 13.56 MHz and operated in mixtures of argon and oxygen. The DC self-bias, the symmetry parameter, the time resolved RF current, the plasma density, and the mean ion energy at the grounded electrode are measured as a function of the driving voltage amplitude and the magnetic field at the powered electrode. Results obtained in pure argon discharges are compared to measurements performed in argon with reactive gas admixture. The results reveal a dominance of the geometrical over the magnetic asymmetry. The DC self-bias voltage as well as the symmetry parameter are found to be only weakly influenced by a change of the magnetic field compared to previous results obtained in a geometrically more symmetric reactor. Nevertheless, the magnetic field is found to provide the opportunity to control NERH magnetically also in geometrically asymmetric reactors. Adding oxygen does not alter these discharge properties significantly compared to a pure argon discharge.

Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code

“…To produce it, one needs a simple external network with a blocking capacitor sustaining the self-bias, and an asymmetry in the sheath behavior. The reactor geometry was chosen to model the experimental facility described in [40,55,56], see Fig. 1.…”

“…Because of this fact and the complexity of the overall electron heating dynamics, we omit such processes from the present numerical model to be able to concentrate on new electron heating/energization mechanisms inherent to the rfMS discharges and to show that they can be well sustained without secondary electron emission. The magnetic field is chosen to model the field relevant to the experimental device described in [40,55,56] and is approximated using the vacuum solution series similar to [69]. The corresponding coefficients are given in Appendix A and it is assumed that due to the low kinetic pressure of plasma in the region where it is well magnetized, the magnetic field modifications due to the plasma currents were negligible.…”

Particle flux characteristics of a compact high-field cascaded arc plasma device

“…The magnetic field strength in the discharge channel significantly increased with the enhancement of C1 current. However, there is a magnetic mirror [22,23] between the target and the front of the anode nozzle that seems to limit the transport of plasma from the plasma source to the target. Due to the mirror effects, the particle flux in the target area decreases with the increase of C2 and C3 currents when the operation current of C1 is fixed.…”

Cluster-Spin-Glass Magnetic Behavior and Morphology in the Coordination Polymer Alloys FeyCo1–yBTT

“…These properties greatly complicate control over magnetic coupling schema as many possible atomic bonds and orientations exist. Alternatively SG behavior may also arise from geometrical frustration, where patterns such as triangular coupling motifs within ordered materials break the symmetry of otherwise antiferromagnetic ground states …”

“…Alternatively SG behavior may also arise from geometrical frustration, where patterns such as triangular coupling motifs within ordered materials break the symmetry of otherwise antiferromagnetic ground states. 18 Topological SGs containing spin centers without structural disorder are less well studied. 19−21 Alternative to creating "spin jammed" triangular topologies, randomly alloyed metal centers in an ordered lattice, in principle, would also provide an avenue for tunable SG properties.…”